Improvements are being made continuously to optical instruments such as cameras having a focusable objective lens. One of the more recent series of improvements is an automatic focusing system for adjusting focus of the lens to an object distance corresponding to the distance of the camera to a remote subject in the field of view of that lens. Typically, an automatic focusing system may use the principle of spatial image correlation wherein a scene imaged by a first auxiliary optical system is scanned by a sensor and the image therefrom is correlated electronically by another sensor with an image from a fixed auxiliary optical system. Such an automatic focusing system has electronics for evaluating the light bundles from images passed through those optical systems and impinging on sensor arrays. Electronics are used to control power for a motor for driving the focusing cell of an objective lens in accordance with the relationship of the images transmitted by the optical systems. Focus of the objective lens occurs when the images from the optical systems are coincident; under such conditions the position of the scanning optical system is related to the position of the objective lens.
Certain of the automatic focusing systems, as described in recently issued United States patents, can be mass produced, are not unduly complex, bulky, and expensive, and are reliable for use in optical instruments or cameras for the mass market. Such systems include a scanning means, which moves an optical axis to sweep an image across a light sensitive array, and which is connected with another similar array of a distance detector. An automatic rangefinder of the type generally described in U.S. Pat. No. 4,002,899 assigned to Honeywell, Inc. and called the Honeywell Visitronics module responds to the two optical systems that bring light from the subject to a detector having a pair of photo sensitive arrays. The module is responsive to the fact that the axes of the optical system are aligned with one another and directed toward the same subject. Such alignment causes the detector to generate a peak pulse which pulse can be used to adjust the focus of the camera lens. One of the optical axes is fixed relative to the rangefinder and camera lens and the other is moveable so as to scan along the other optical axis. Rangefinding is accomplished by triangulation and comparison of the image from the fixed axis with the image from the scanning axis. By means of suitable electronic circuitry the peak signal can be converted to a control signal for the focusing motor.